The present invention relates to a system for opening and closing a door. When used in this sense, the word "door" is intended to have a broad meaning including any closure member, such as a residential or industrial garage door or gate.
In the past, door opening systems have relied heavily on the use of electromechanical limit switches to determine the "open" and "closed" position of the door for de-energizing the motor driving the door. Further, pressure switches or mechanical "trips" have been used to sense obstructions to movement of the door during opening or closing. One of the disadvantages of such prior system is that the limit switches had to be accurately installed for sensing the open and closed positions of the door. If the operation of these switches were in any way impaired or if they became dislodged from their original positions, the system would not operate as intended.
According to the present invention, the shaft driven by a reversible motor used for opening and closing the door is provided with at least one reflective surface. An optical source/detector is used to generate a train of pulses representative of the rotation of the drive shaft. These pulses are fed into a programmable counter circuit which is incremented for each pulse when the door is opened. When the counter circuit reaches a predetermined count, the motor is de-energized.
The counter circuit is programmable so that it also may count down, and when the operate push button is pushed a second time, the counter circuit is decremented by the pulses from the optical detector representative of rotations of the drive shaft. When the counter reaches a zero count, the door has been returned to its original position, and the motor is again de-energized.
A slip clutch is provided between the motor and drive shaft, so that if an obstruction is encountered by the door and it stops, the clutch will slip. A rotation monitor circuit generates a signal when the door is obstructed, and if the door was being opened when the obstruction was encountered, the motor is simply de-energized to stop the door. On the other hand, if the door was being closed, the rotation monitor reverses the motor and the door is opened.
The counter circuit may be programmed to detect any predetermined number of counts; and the open and closed positions of the door may therefore be accurately determined, depending upon the pitch of the thread cut in the drive shaft, and the number of reflective areas around the circumference of the shaft.
The system also provides a "park" cycle in which, if the operate button is actuated during opening or closing of the door, the drive motor is de-energized and the door is stopped. The next time the push button is actuated, the movement of the door will be reversed until it completes a full open or close cycle, or until the operate push button initiates another "park" cycle. The system also includes timing circuitry for operating an electric light as long as the drive motor is energized, and for a predetermined time after it is de-energized.
The system also includes circuitry for detecting and compensating for mechanical drift or coast due to inertia or other external forces. Additional circuitry permits the system to stop and reset if an obstruction is encountered within the last two inches of the original closed position setting.
Other features and advantages of the present invention will be apparent to persons skilled in the art from the following detailed description of a preferred embodiment accompanied by the attached drawing.